Gypsy Moth Defoliation of Hybrid Poplar: Effects on Growth, Carbohydrates, and Root Demography

Kosola, K.R., D.I. Dickmann, D. Parry, C. Easley, E. Duncan, C. Lynn, E.A. Paul

Presented at the All Scientist Meeting (1999-07-20 to 1999-07-21 )

Defoliation effects on trees should cascade through the entire ecosystem, altering fluxes of carbon, water, and nitrogen as well as changing the quality and quantity of resources available to herbivores and to the soil biota. We examined the dynamics of changes in tree carbon allocation during and immediately after defoliation of hybrid poplar caused by gypsy moth. We found symptoms consistent with declining carbon allocation to starch synthesis and root production caused by defoliation. Both root production (Fig. 1A) and total nonstructural carbohydrates (TNC) in all root, trunk and twig samples (Fig. 2) were lower in the defoliated treatment. The effects on starch production were transient, and disappeared by the end of that same growing season. Contrary to our expectations, root survivorship was not affected by defoliation (Fig. 1B).The timing of defoliation and the phenology of poplar both play a role in determining the impact of defoliation on the tree. Gypsy moth, as an early-season defoliator, does not remove leaves late in the season when poplar C allocation is primarily directed belowground. Furthermore, even during the highest population densities of 1997, the leaf meristems and youngest, unexpanded leaves were not eaten by the caterpillar, leaving a large potential leaf area ready to expand and photosynthesize as soon as pupation started. The trees were poised to recover very rapidly following defoliation. As a consequence, the LTER poplars were relatively tolerant to defoliation by gypsy moth.

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